The present invention relates to a continuous casting machine that is used to continuously produce copper ingots having a diameter of, for example, 200 mm or a belt-wheel type continuous casting machine that continuously produces ingots having a smaller sectional size that are used for producing copper or aluminium rods, to a molten metal surface level detection system which is best-suited for maintaining the surface level of molten metal poured in such a casting machine at a constant level with a high accuracy.
As shown in FIG. 1, in the aforesaid continuous casting machines in general, molten metal 1 is first fed in a reservoir 2 and, then, the molten metal 1 is poured from the resevoir 2 through a gate 3 thereof into a molding device 4 in which cooling water 5 is passed through an internal cavity formed therein, and it is very important to maintain the molten metal surface 6 at a constant level with a high accuracy in view of the quality control of the ingots to be produced therefrom.
Also, in the aforementioned belt-wheel type continuous casting machine (not shown) in which a casting wheel that is rotated in a predetermined direction is provided in a position corresponding to the position of the aforesaid molding device 4 and a belt that goes round in the same direction is provided on the outer side thereof in such a manner that the molten metal is poured from said gate 3 into the space defined by said wheel and belt, the surface of the molten metal poured in said space must be maintained also at a constant level.
For this purpose, it is necessary to detect the level of said molten metal surface 6 for controlling the same and, heretofore, the surface level has been controlled in such a manner that a worker or an operator visually detects the molten metal surface 6 and, then, manually operates a pour controlling pin 7, on the basis of such a visual detection, to increase or decrease the quantity of molten metal flowing into the gate 3 from the reservoir 2.
Therefore, in such a system, not only a quality improvement of ingots has been far from expected because some variation is encountered with each different operator in the controlling operation, but also operators in performing the controlling operation have been subjected to severe working conditions in extremely inferior environment near the casting machine heated to a high temperature. Thus, development of an unattended automatic molten metal surface level detection system has long been desired.
However, as mentioned herein, since the gate 3 directly extends towards the molding device 4 below the same and the molten metal pours out therefrom at a high speed, only a small space could be reserved therein for the provision of surface level sensors that are used to detect the molten metal surface level. Further, since the molten metal is a fluid having a temperature above 1,000.degree. C. and a burner is provided for heating the gate 3, the thermal conditions are much unfavorable to the installation of measuring instruments and, thus, it has not been possible to apply such level sensors conventionally adopted to the molten metal surface level detection system in continuous casting machines.
Therefore, as shown in FIG. 2, it has been proposed to provide a radiation source 9 in the vicinity of the molten metal surface portion 8 including the surface 6 thereof to irradiate radioactive rays onto said molten metal surface portion 8 so that the dosage of radiation 10' permeating the same is counted by means of a dosimeter 11 at a predetermined time interval and the variation of the molten metal surface 6 is detected on the basis of the thus counted dosage.
However, to improve the accuracy in the detection of the molten metal surface level, it is necessary to increase the dosage of radiation permeating said molten metal surface portion per unit of time and, for this purpose, a more powerful radiation source must be provided or the counting time of the dosimeter must be extended.
However, trying to use such a more powerful radiation source requires a use of a larger-sized source and, thus, consumes an unreasonably large space for the installation thereof. While, if the counting time is extended, the detection system becomes unable to keep track of rapid changes in the molten metal surface 6 and, thus, an improved quality control cannot be expected.
In addition, the gate 3 or mold 4 is frequently replaced in the casting machines of the aforementioned type, and since the radiation device is disposed at the site where the aforesaid replacement works are performed, a severe limitation must be imposed on the installation of such a radiation device from a viewpoint of safety and, due to such a safety requirement, the aforecited detection system using radiation has not been satisfactory, in view of its funciton as a surface level sensor.